A hot water bottle is one of the cheapest ways to put real heat into a cold bed or chair. You fill it from a kettle or pan of hot water, seal the stopper and tuck it against your body or between the sheets, where it radiates warmth for a few hours before slowly cooling. Most UK versions hold one to two litres, cost around five to fifteen pounds, and last for years if you replace them before the rubber perishes. In a winter power cut it comes into its own, because you can heat water on a gas hob or camping stove and warm a bed without any electricity at all.
A wool blanket takes the opposite approach. Rather than adding heat, it insulates, trapping the warmth your body already produces in a thick layer of wool or wool-blend fibres. A decent one weighs one and a half to two and a half kilograms, costs roughly fifteen to fifty pounds, and keeps working reasonably well even when slightly damp, which suits Britain's wet cold. The two are not really rivals: one is an active heat source that fades over a few hours, the other a passive insulator that keeps you warm for as long as you stay wrapped in it. In practice the strongest cold-weather setup usually uses both together.
